1. Field of Invention
The invention relates to electromagnetic brakes and more particularly to an electromagnetic brake used for electric walker, the electromagnetic brake having an improved handle which is produced in a simple process without involving of soldering so as to greatly reduce the manufacturing cost.
2. Description of Related Art
There have been numerous suggestions in prior patents for electromagnetic brake. For example, U.S. Pat. No. 4,820,946 discloses an electromagnetic brake in which there is provided a single mechanism capable of both adjusting the brake spring force and the releasing the brake spring force entirely when necessary.
In addition, a conventional electromagnetic brake is shown in FIGS. 1, 2 and 3. The electromagnetic brake comprises a cylindrical housing 10 including a pin 12 and a brake spring (e.g., coil spring) 11 put on the shank of the pin 12. A handle 13 is provided on a top of the housing 10. The handle 13 comprises on its top a substantially disc shaped member 132 and a staged hole (not numbered) on a center. A washer 14 is snugly placed in the hole of the disc shaped member 132. A screw 15 is fastened through a central threaded hole (not numbered) of the washer 14 into a threaded hole (not numbered) of the shank of the pin 12 to pivotably secure the handle 13 to the housing 10 with the spring 11 being compressed between the enlarged head of the pin 12 and a top of an internal compartment of the housing 10. As such, the handle 13 is pushed outwardly by the expansion force of the spring 11. A coil 150 in the form of a ring is provided in the housing 10. A disc shaped armature plate 16 moveably provided under the coil 150 comprises six equally spaced recesses 161 along a peripheral edge. A disc shaped bottom plate 18 has a central opening (not numbered) and six equally spaced through holes (not numbered) between a peripheral edge and the opening. A plurality of (e.g., three) screws 17 are driven through the plate 18 and the recesses 161 into the housing 10 for slidably fastening the components disposed between the plate 18 and the coil 150 as detailed later. A friction disc 19 having a central opening (not numbered) is provided between the armature plate 16 and the plate 18. The friction disc 19 is operatively connected to a drive means (e.g., shaft of a motor (not shown)) to effect a braking. In a brake released operation, electric voltage is applied to the coil 150 to generate a magnetic field to attract the armature plate 16. As such, the armature plate 16 is disengaged with the friction disc 19. The friction disc 19 is free and the brake is thus released. A user may further pivot the handle 13 to enable a trigger switch 131 provided on top of the housing 10 proximate an edge of the disc shaped member 132. The enabled trigger switch 131 thus causes the electromagnetic brake to apply the brake.
As shown in FIG. 2, a plurality of steel balls 134 are rotatably sandwiched between half holes (not numbered), e.g. arcuate grooves as shown in FIG. 1, of the handle 13 and half holes (not numbered) of the disc shaped member 132. However, a precise alignment between the respective half holes is required. Otherwise, the desired rotation capability of the steel balls 134 can not be achieved. It is typical of securing the disc shaped member 132 onto the handle 13 by soldering. However, the soldering is a troublesome, time consuming process.
As shown in FIG. 3, a maximum pivotal angle of the handle 13 is about 15 degrees as defined by two adjacent rods 101 projecting from the top of the housing 10. When the handle 13 is pivoted about 15 degrees relative to its other operation point (as indicated by dashed lines), the contact 1311 of the trigger switch 131 is aligned with an indentation 133 at an edge of the handle 13. Thus, the trigger switch 131 is disabled. A further pivoting of the handle 13 will cause its edge to contact the contact 1311 of the trigger switch 131. And in turn, the trigger switch 131 is enabled to cut off the power. As a result, the coil 15 is not energized, resulting in a brake applying of the electromagnetic brake.
However, the well known electromagnetic brake suffered from several disadvantages. For example, both the disc shaped member 132 and the handle 13 are required. Further, their half holes are required to be precisely aligned when they are assembled. Hence, the manufacturing processes are complicated. Moreover, the disc shaped member 132 and the handle 13 are separate members prior to soldering together. Thus, more materials are consumed in the manufacturing processes. Further, high precision is required, resulting in an increase in the manufacturing cost.
Thus, it is desirable to provide an improved handle of electromagnetic brake in order to overcome the drawbacks of the prior art.